Process for preparing a liquid oxygen explosive



2,812,246 1 PROCESS FOR PREPARING. A LIQUID OXYGEN EXPLOSIVE Samuel W. Martin, Oak Park, 111., assignor to Great Lakes Carbon Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application August 12, 1955, Serial No. 528,120

3 Claims. (Cl. 52-1) This invention relates to a process for preparing liquid oxygen explosives. More particularly, this invention relates to a process for preparing liquid oxygen explosives in which a specially prepared absorbent carbon is employed.

Mixtures of highly volatile oxidizing agents such as liquid oxygen, liquid air or liquid ozone with a combustible substance, such as finely divided carbon, have previously been proposed as explosives. This typeof explosive is ordinarily employed by forming cartridges of the finely divided carbon, soaking the cartridges in liquid oxygen or other volatile oxidizing agents and then within a short time using the saturated cartridges in blasting operations. This kind of explosive is not only powerful but has certain advantages over other types of explosives. Since the components of these explosives are mixed at the site Where they are to be used and since these components are not alone likely to explode, all hazards resulting from the transportation of an explosive mixture are avoided. Also, if the prepared charge fails to detonate for any reason the charge is rendered harmless by the subsequent evaporation of the volatile oxidizing agent. However, the employment of explosives of this type in the past has been dangerous due to the fact that the mixture of carbon and liquidoxygen, in most cases, is easily detonated by impact or friction. Accordingly, there is a great danger of premature explosions caused by rocks or other objects falling on the explosive mixture while it is being lowered into drill holes or by other shocks accidentally transmitted to the mixture.

Attempts have been made to desensitize liquid oxygen explosives by diluting the absorbent carbon with inert absorbents. For the same reason attempts have been made to fire proof the absorbent carbon by coating or impregnating with various chemicals. These attempts to desensitize or fire proof the carbon have not only been costly but also have not been entirely effective.

It is therefore an object of this invention to provide a process for producing an explosive of the liquid oxygen type which without the addition of desensitizing or fireproofing agents, is less sensitive to detonation by impact or friction than any previously known liquid oxygen explosives.

It is a further object of this invention to provide a process for producing a liquid oxygen explosive, which despite the fact that it is relatively safe to handle, is nevertheless effective, when properly detonated, with respect to its disruptive or shattering properties. 1 s

It is a further object of this invention to provide a process for producing a liquid oxygen explosive, in which a hard, granular carbon is prepared which is sutficiently absorbent with respect to liquid oxygen or similar volatile oxidizing agents to function safely and effectively in said explosive.

The above objects as well as others which will become apparent upon understanding of the invention as herein described, are accomplished by the flash oxidation-ca}, cination of finely divided swelling bituminous coals at a temperature above 800 C. and then causing liquid oxygen or other equivalent volatile oxidizing agent to be absorbed by the resulting hard, granular absorbent carbon product. The method of oxidizing and calcining the coal nitcd States Patent.

particles will be described herein and isso conducted that the' resulting absorbent carbon product will have a bulk density of 10-20 lbs. per cu. ft.; a volatile content of no more than 5% by weight; ash content of about 8% to about '15 by weight; and particle size of at least 70% less than 200 mesh.

The term flash oxidation-calcination as used herein and in the appended claims may be defined as a method whereby finely divided particles of swelling bituminous coal are subjected to a very rapid upheat rate, estimated to be in excess of 1000 C. (particle surface temperature) per second, into the temperature range of about 800 C. or higher. .This rapid upheat of the coal particles is conducted in the presence of air or other oxygen-containing or oxidizing gas, which serves not only to burn the volatile matter evolved from the coal thereby making the process self-sustaining but also serves to oxidize a portion of the fixed carbon of the resulting charred particles to provide the proper structure which renders the final product suitable for absorption of liquid oxygen. The term flash oxidation-calcination further connotes the necessity for heating the coal particles at a sufliciently rapid rate so as to initially expand the individual particles even though they may be subsequently reduced in overall size by oxidation. The bulk density of the final product must be maintained at a value of 10-20 lbs/cu. ft. If

-the coal particles are heated at a sufl'iciently rapid rate into a temperature range of 800 C. or higher, the particles become plastic and swell due to devolatilization; this type of operation is essential for satisfactory production of the absorbent carbon under consideration.

The'step of expansion and oxidation is best performed by feeding a crushed and sized swelling bituminous coal into a rapidly moving stream of oxidizing gas at a temperature above about 800 C. (reactor temperature). This results in an initial expansion and devolatilization of the coal particles together with the burning of the volatile matter and a portion of the fixed carbon in the coal. The 'oxidization and heating are controlled so that the resulting product has an ash content of about 8% to about 15% by weight (depending in part on the ash content of the coal); the particles of the product will have a size within a range of at least 70% less than 200 mesh. The flash oxidation-calcination operation must also be conducted so as to produce particles having 5% or less by weight of volatiles.

While it is preferable that the source of heat used in each of the stages be the particle itself, it is conceivable and within the contemplation of this inventioin that a substantial portion of the heat may be supplied by some 7 outside source or auxiliary fuel. The most rapid upheat rates are, of course, obtained using the particle itself as the source of heat.

The types of coal which are suitable for the manufacture of the absorbent carbon which is employed in the practice of the present invention are broadly classified as swelling bituminous coals. These coals fall within the types of coal set out in the Encyclopedia Britanica, vol. 5, page 872 (1948): a

Any swelling bituminous coal having a volatile matter content in excess of about 12% by weight will be suitable for-the preparation of the absorbent carbon employed in the present invention. These types of coal are characterized by softening when heated through the plastic state and will swell if the volatile matter of each' particle is s loin 9 t a ufii i t y high rate- 'sorbent carbon is of a smaller particlesize.

The aforesaid bituminous coal employed in preparing the absorbent carbon should not have too high an ash content since mineral impuritiesintoo. greatanramounh may resultinacarbon of unfavorabledetonating,charam teristics. In; general, itmaybestatedlhat no;.coal:should. be. used. whichwill res u1t:in. an absorbent carbornp roduc-tv having an ash content of more than 15% .by. weight,,

In preparing the, bituminous coal. described. aboverfor thefirst stage flash-calcination op,eratio n, the coal, must. be. suitably ground or milled to produce finely divided. particles, This involves the.use.of a Raymondlring roller. mill, Babcock andwilcoxball ring mill: or other .appro.-. priate 'pulverizing apparatus which will, reduce. the.. c0.a.L to. a particlesize; of; about. 95 100..mesh andpreferr. ablyabout 75. to, 95% 200.mesh. It has been found. thatthe latter-size offeed is to,.be preferred inporder, to. produce from I the. coal. at .final absorbent. carbon product. which willthavera particle. size. of atleast 70% .-'20.0. mesh I also contemplate under certain circumstances the millingand,classification (by either. dry. or wet methz ods) ofthe. bituminous feed.

In ,preparingthe. absorbent carbon by the process, de.e

scribedherein, I havefouiid that,particiularlybeneficialr results are to beobtained by maintaining the moisture. content of the raw. material at a value of, less. than 5% by, weight. Excess moisture in the bituminous, coal fed to the. unit in which the flash-calcination is, conducted necessitates.vaporization of the. water to,z-'a;ternperature.- above. 800 'C., or whatever reactor temperature used;

whichsharply reduces the'rate of temperature rise oflthe,

coal particles v Often this Il'lllSlLbGzdOIE by. burning-addi -s tional fuel in theunit since excess moisture inthe. par-l ticles reduces thetemperature .of the op eratiomto :a .point where thedesired results areznotobtaineda Theabsorbentcarbon, whose process ofmanufactureis; described herein, should have a particle size of atleast. about-70% 20.0..mesh.. A finer-particle: sizermaybe appropriatefoncertain blasting operations. Forexample, an explosive. of; higher brisance .is. obtainedwhen the,- ab: Howeven, when suchsmaller particle size,is;- employed itxmay be; necessary to adjustother physical characteristics iof the;

particles to, maintaina sufficiently low .impactresistance;

forsafety reasons Another requirement .of,.the absorbentcarbon produced" in this inventio,n-.is. thatit have a volatilecontenLofrno more than 5 by weight as determined ;by AS'TMrPro,-. cedure ,No. D271.-A8..

A further requirement. of. the'absorbent, carbon pro: ducedby .the process of. my-invention is.that.it-.have.-a bulk density between 10. andz20, lbs. per cu..ft. Bulk density values are determined by permitting,thesproduet to fall freely into a graduatedcylinder andmeasuringthe loose-settled volume of a given weight of the l'irotluet.

The absorbent carbonwhich is. used immy invention has aiblack to. grey fluffy appearance rand isressentially non activated. Under. the microscopesome,ofathesevparr ticles appear, to. contain numerous perforations or; chan nelsjn or nearthe surface .ofeeach particle; others'fappear. to have a bubble-like surface structure with:.or= without the aforementioned perforations or channels; allof'which are presumably caused by devolatilizationsaud oxidation during the flash heat treatment of the coal particles. This structure which is formed during the flash oxidation-cal: cination operation-is considered essential; toiprovideim carbon which when caused tot absorb :liquid oxygenewil'l' give an explosive of desirablecharacteristics.

In a preferred embodiment of the invention a quantity offWilliams coal, Coking Seam No. 6 from-'West Kentucky, was pulverized to 84% 200 mesh; the moisture content of the product beingless than 5%'-by weight; a horizontal tube furnace of 30'inches inside= diameter-Was preheated toa temperature of about 1450 C2 by means of combustion of oil or gasafter which the coal'wasblow into the furnace with suflicient quantity of air-sothatthemaximum furnace temperature was in the range of 1350- 1650 C., and also in suflicient amount to reduce the volatile matter of the coal to .-3.- to 4% by weight, the originalacoa-l havinga lvolatile content of.37.8%. The product was cooled by arwater; quench at the end of the furnace ,and. was collected. in av cyclone. The product had;the .followingproperties Bulk density 15.3 lbs/cu. ft. Volatile-content; 4.2%;

Ash content 9.5%.

Particle size 75% 200 mesh.

The hard; granular-,=finely divided absorbent carbon produet was-then packed-in fi reproofed cloth cartridges and saturated-with liquid' oxygen to:produce a safe but eflt'ectiveexplosive composition.

In a further embodiment of the invention the Williams coal mentioned above was-"ground to l00'mesh and w-as' passed" into-the'top' of a verticaltubular furnace which had previously-been preheated'to 1100" C. The coal' particl'es' were suspended in a suflicientamount" of air-iiiorder to-reducethe volatile content of the coal to ab'out-3 %f"by*weight -andto burna sufficient amount of the fixed'carbonin the'coal-so that the final'product'had an-aslr-contentof -about'-9%-' by weight." As in the case of 'the'foregoing-operationthe product Was cooled by a water 'quench and collected in' a cyclone. size=-of"the"product-was 73%- 200 mesh. The bulk densityof the'productwas 17lbsz/ cu.- ft. and the volatile content'- was-3i2%=by-weightr The hard, granular,

finely divided," absorbent carbon produced was then.

packed in-fireproofedclothwartridges and saturated-with liquid oxygen 'to"producea' safe but effective explosive composition:

In a further-butt less preferred embodiment of the in'vention;- a*bituminous coal-having a volatile content greater than"20% by-weighfiwas fluidized'in a furnace preferably preheated'to'a= temperature of about 850 C. Byregulation of,the-qu,antityand velocity of the'air entering-fthe-fluidization unit .the low'bulk density particles which resultare'bl-owrr out of the top of the unit and collected in a product cyclone, for exampleafter the product has ireached-abullc'density of less than 20 lbs/cu. ft. In-this'"type-of operation a larger 'amount of fine particles willbe, found in the" product due to the attrition incurred-in the 'fluidizing unit: When the absorbent'carboniproduced-ispackedjnthecloth cartridges and saturated with liquid-"oxygena slightly less stable explosive with a higher-brisanee is'produced.

The reactor"- temperatures setforth inthe various embodiments ofrny'invention; are the apparent atmospheric temperatures;;rather; than particle temperatures, and are measured*-by- .means of'thermocouples inserted intothe interionof the-reactors through ceramic sealed wells in the reactor walls.

lr'r' order to further illustratehthe invention butwith no intention -of:being "limited thereby, the following examples are-set forth in which various coals were preliminarily ground 1 to suitable particle-size, with controlled moisture content, after which thecomminuted'coal was fed to a stationary horizbnta'ltubular furnace Whichhad been preheatedi to' a-certairr-temperature at which the. flash oxidation -calcination"operation was to be; conducted. The produet'was cooled byspraying 1 or fog ging' with 'Water eitherat'the end of the-reaction-tube or just" prior .to the entry of the product into the cyclone. The absorbent carbon obtained was then-saturated with liquid oxygen and detonatedwnder' controlled conditions permitting measurementofvarious explosive characteristics.

acterizing nry'explosive"or 'the carbon used therein;

Detonationyelocitywas determined by measuring the time interval: which elapsed'between the breaking of two copperwires-aknown distanceapart: This time interval was measured with a Hewlett Packard type '522 interval The particle The; following is an explanation'gofi terms-used in char- 7 timer. Wires to be broken were No. 30 copper wires threaded through a 4 ft. long cartridge, there being a distance of 3 ft. between the two wires. A piece of pr-imacord was inserted into the end of the cartridge so that it was about 4" from the start Wire. This distance between the primacord and wire is necessary in order to be sure that the wire is broken by the carbon and oxygen explosive rather than the primacord.

Low-velocity impact resistance indicates the resistance of the explosive composition to detonation by accidental impact and was determined in accordance with the procedures described in U. S. Bureau of Mines Bulletin 472, pages 20-27. The explosive composition of my invention has a low-velocity impact resistance of 1400 ft.-lbs. or more. In other words, this impact is required to accidentally detonate the composition.

Burning in semi-confinement indicates what may be expected if the explosive composition should be ignited after it has been loaded into the drill hole. A 1% diameter pipe was capped at both ends and provided in one cap with varying degrees of pressure relief by drilling various diameter holes. An explosive mixture contained in the pipe was then ignited with a slow burning fuse and success or failure to detonate was noted. The smaller the orifice necessary for the burning to cause an explosion, the safer the explosive.

"Oxygen absorption and retention.The ability of the absorbent carbon to absorb and retain liquid oxygen was determined by immersing a 2 ounce sample of the carbon contained in a fire-resistant cotton bag in liquid oxygen. After ten minutes the bag and contents were removed and immediately weighed to determine the initial oxygemcarbon ratio. A timer was then started and the bag was left on the balance to determine the time required for evaporation to decrease the oxygen-carbon ratio to 2.0. The value obtained serves as an index of the retention times that can be expected in commercial blasting operations wherein the cartridges and filling methods employed result in longer retention times. A long retention time is desirable since it allows more time to prepare the explosive charges prior to their detonation.

Example N0. 1

A sample of Williams coal, seam No. 6, which is a swelling, bituminous coal, having a volatile content of 39.8% by weight was milled to 70% 200 mesh. A tubular furnace of 30 inches inside diameter was preheated to a temperature of about 1000-1200 C. by burning gas in a burner placed in one end of the furnace. A stream of the coal was then fed into the furnace at a rate of 1200 lbs./hr. together with 1500 cu. ft./minute of air which was suflicient to reduce the volatile content of the coal down to about 4% by weight and burn a sulficient amount of the fixed carbon so that the yield of product collected in the cyclone was about 20% based upon the original coal. The product obtained had an ash content of 9.5%, a particle size of 73% -200 mesh, and a bulk density of 15.8 lbs./ cu. ft. Oxidation absorption tests showed the initial oxygenzcarbon ratio to be 3:1 and the oxygen retention time 11.7 minutes. Tests on liquid oxygen explosives prepared with this carbon showed the low-velocity impact resistance to be more than 1450 ft.-lbs. In semi-confinement tests, detonation failed to occur using an orifice of A" in diameter. The detonation velocity of the explosive was found to be 15,600 ftJsecond.

Example N0. 2

A sample of Ditney Hill coal was ground to 86% -200 mesh. This coal was also a swelling, bituminous coal and had a volatile content of 35.5%; ash content 4.6%. This coal was fed to a 4 inch tube furnace (preheated to 1100 C.) at a rate of 50 lbs/hr. with 40 cu. ft./minute of air. The product was cooled by water fogging prior to entry into the cyclone. A hard, granular absorbent carbon was obtained in a yield of 28% based on the dry weight of the feed. This carbon had an ash content of 10.1%, a volatile content of 3.2%, a bulk density of 11.1 lbs./cu. ft., and a particle size of -200 mesh. Oxygen absorption tests indicated that the carbon had the initial oxygenrcarbon ratio of 4:1 and an oxygen retention time of 11.8 minutes." Tests made on liquid oxygen explosive prepared with this carbon showed the explosive to have a low-velocity impact resistance of more than 1200 ft.-lbs. Burning in semi-confinement tests failed to detonate the explosive using an orifice of A" diameter. The detonation velocity of the explosive was 14,050 ft./second.

Example No. 3

For purposes of comparison a carbon prepared from wood bark and commonly used in liquid oxygen explosives after chemical treatment to make it fireproof was subjected to the aforesaid tests. Using a non-fireproofed sample, it was found to have a bulk density of 12.0 lbs./ cu. ft., and an ash content of 1.9%. Oxygen absorption tests indicated that its initial oxygenzcarbon ratio was 3.5 and oxygen retention time 12.0 minutes. A lowvelocity impact test on a liquid oxygen explosive prepared with this carbon produced explosions at 930 ft.-lbs. In a semi-confinement test the explosive detonated when using an orifice of A" diameter but not with an orifice of diameter. The detonation velocity was 18,000 ft./second.

The explosives prepared according to my invention and described in Examples 1 and 2 were found to be highly effective and unusually safe despite the lack of any fireproofing treatment of the absorbent carbon.

It is to be understood that the absorbent carbon employed in my invention may be classified (or milled and classified) by dry or wet methods in order to regulate the oxygen absorption characteristics. Also it is contemplated, when considered desirable, to activate the absorbent carbon product by means well known in the art, to increase its ability to absorb liquid oxygen.

It should also be understood that containers other than cloth bags may be used as cartridges in my method for producing the explosive. Such materials may be polyethylene, aluminum and other non-sparking metals.

Having thus described the nature of my invention, I claim:

1. The method of producing a liquid oxygen explosive which comprises preparing a hard, granular, essentially non-activated absorbent carbon by the thermal expansion of finely divided bituminous coal suspended in an oxygen containing gas maintained at a temperature between about 1200 to 1700" C. and at an upheat rate higher than 1000 C./second (particle surface temperature), said carbon having the following properties: bulk density of 10-20 lbs./ cu. ft., volatile content less than 5% by weight, ash content of about 8% to about 15% by weight, and particle size at least 70% less than 200 mesh; and thereafter causing liquid oxygen to be absorbed by the resulting absorbent carbon.

2. A process according to claim 1 in which the expansion zone is maintained at a temperature between 1350 to 1650 C.

3. A process according to claim 1 in which the coal has a volatile matter content of about 30 to 40% by weight.

References Cited in the file of this patent UNITED STATES PATENTS 1,960,907 Holderer May 29, 1934 2,556,859 Vesterdal June 12, 1951 2,721,184 Voorhies Oct. 18, 1955 OTHER REFERENCES Industrial Carbon, C. L. Mantell, D. Van Nostrand, Inc, N. Y. (1946), pp. 231-241. (Copy in Div. 64.) 

1. THE METHOD OF PRODUCING A LIQUID OXYGEN EXPLOSIVE WHICH COMPRISES PREPARING A HARD, GRANULAR, ESSENTIALLY NON-ACTIVATED ABSORBENT CARBON BY THE THERMAL EXPANSION OF FINELY DIVIDED BITUMINOUS COAL SUSPENDED IN AN OXYGEN CONTAINING GAS MAINTAINED AT A TEMPERATURER BETWEEN ABOUT 1200* TO 1700*C. AND AT AN UPHEAT RATE HIGHER THAN 1000*C./SECOND (PARTICLE SURFACE TEMPERATURE), SAID CARBON HAVING THE FOLLOWING PROPERTIES: BULK DENSITY OF 10-20 LBS./CU.FT., VOLATILE CONTENT LESS THAN 5% BY WEIGHT, ASH CONTENT OF ABOUT 8% TO ABOUT 15% BY WEILGHT, AND PARTICLE SIZE AT LEAST 70% LESS THAN 200 MESH; AND THEREAFTER CAUSING LIQUID OXYGEN TO BE ABSORBED BY THE RESULTING ABSORBENT CARBON. 